The present invention relates, in general, to photonic devices, and more particularly to improve monolithically integrated photonic devices incorporating monitoring photodetectors and methods for fabricating them.
Many optical systems, such as, for example, those incorporating or utilizing Passive Optical Networks (PON), require that a single optical fiber be used for both sending and receiving information at multiple wavelengths. In the past, such a capability has been difficult to achieve, particularly in a cost-effective manner, for the combination of a multiplicity of discrete photonic devices that will all have access to a single fiber has presented fabrication problems that have made such arrangements too expensive. The market for PON systems is extremely price sensitive, with the result that the highly desirable, wide range of functions that such networks can make available have not been economically feasible. Similar difficulties have been encountered with the use of multiple photonic devices in other optical systems, such as high definition DVD's, for even in such applications the required high level of functionality is not easily attainable through the use of discrete photonic devices.
Because photonic devices such as lasers tend to change their characteristics with changing environmental conditions, it is desirable to monitor their operation, but such monitoring is not easily achievable when using discrete devices, particularly when the devices are extremely small.